1. Field of the Invention
The present invention relates to an electrical connector having a plus signal terminal, a minus signal terminal, and a ground terminal, particularly to an electrical connector for transmitting differential signals at a high speed.
2. Related Art
An automobile vehicle is equipped with electronic instruments such as a navigation system. The navigation system has a main unit for calculating a present position of the vehicle and a display for indicating the present position and a destination position of the vehicle. This type of display requires high resolution and needs to indicate the present position in real time.
Signals supplied from the main unit to the display tend to increase in quantity. Therefore, various types of high-speed signal transmission processes have been applied to such navigation systems. There are a single end type (unbalanced type) and a differential type (balanced type) in conventional signal transmission processes.
The single end type has a single signal lead and a ground lead for recognizing “HIGH” and “LOW” of digital signals by a potential difference between the leads, which has been used generally.
Meanwhile, the differential signal type uses two signal (plus and minus) leads for recognizing “HIGH” and “LOW” of digital signals by a potential difference between the leads. Each signal of the two leads is equal to each other in voltage but, offset by 180 degrees in phase from each other. The differential signal type can cancel noises generated by the two leads at a receiver side to allow a high speed signal transmission as compared with the single end type.
To achieve high-speed transmission of differential signals, Japanese Patent Application Laid-open No. 2002-334748 discloses connectors like ones shown in FIGS. 38, 39. A connector 101 or 102 has a plus signal terminal, a minus signal terminal, and a ground terminal.
The connector 101 shown in FIG. 38 has a housing 109, a plus signal terminal 103, a minus signal terminal 104, and a ground terminal 105. Each of the terminals 103, 104, and 105 is positioned at each corner of an isosceles triangle.
The connector 102 shown in FIG. 39 has a housing 110, a plus signal terminal 106, a minus signal terminal 107, and a ground terminal 108. Each of terminals 106, 107, and 108 is formed in a metal plate having a rectangular section with a comparatively larger thickness. The ground terminal 108 has a width larger than those of the plus signal terminal 106 and the minus signal terminal 107.
In the connector 102 shown in FIG. 39, the plus signal terminal 106 and the minus signal terminal 107 are positioned to be spaced from the ground terminal 108 in parallel with the ground terminal 108 along a longitudinal direction of the terminals.
The connector 101 or 102 shown in FIG. 38 or 39 has the single ground terminal 105 or 108 that cooperates with the plus signal terminal 103 or 106 and the minus signal terminal 104 or 107 for signal transmission.
The navigation system mounted in the vehicle preferably has a plurality of the displays which are arranged each in a front seat or in rear seat. Thus, a cable connecting the main unit to the display for high-speed differential signal transmission may become longer. Meanwhile, a connector for the high-speed transmission needs to achieve a less signal loss.
In the conventional connector 101 or 102, a current flow for signal transmission in the plus signal terminal 103 or 106 generates an induction current in the ground terminal 105 or 108. In turn, the induction current generates another induction current in the minus signal terminal 104 or 107 since the ground terminal 108 corresponds to both the plus and minus terminals.
Furthermore, a current flow for signal transmission in the minus signal terminal 104 or 107 generates another induction current in the ground terminal 105 or 108. These induction currents have an adverse effect to each other, causing an increased loss in signal transmission.